1. Technical Field of the Invention
The present invention relates to packet communications and, in particular, to the inverse multiplexing of asynchronous transfer mode (ATM) cells within ATM communication networks.
2. Description of Related Art
Historically, separate methods and protocols were used for transporting information within a Local Area Network (LAN) versus a Wide Area Network (WAN). Due to a large number of separately controlled and configured networks, such a distinction between the associated networks created inter-working problems as user data are transported between multiple incompatible networks. As a result, the Asynchronous Transfer Mode (ATM) standard has been introduced as a worldwide standard to allow interoperability of information, regardless of the "end-system" or type of information, between associated networks. Using ATM, user information to be sent is segmented into fixed length cells, and transported to and re-assembled at the destination. Being fixed length allows the cells to be transported in a predictable manner through the network and enables the associated switches and transportation mechanisms to achieve high-speed and flexible communications.
Now referring to FIG. 1, there is shown a block diagram of an ATM network 10 illustrating two ATM switches with multiple narrow bandwidth T-1 communication lines connected therebetween. A first ATM switch 20 receives a stream of ATM cells over a high-bandwidth incoming communication link 30, such as an OC-3. Although it is desirable to switch the received cells over another high band-width connection to a second ATM switch 50, due to a lack of communication resources, the first ATM switch 20 may have to utilize other lower speed communication links. As an illustration, the first ATM switch 20 transmitted the received cells over multiple slower speed T-1 links 40 to the second ATM switch 50. T-1/E-1 communication links have been commonly utilized by a Public Switched Telephone Network (PSTN) to transport voice and data within the United States, as well as world-wide, and are already well placed and available throughout service areas. With no other connections available, the first ATM switch 20 partitions (de-assembles or distributes) the received ATM cells and transmits the de-assembled cells over a number of slower T-1/E-1 communication links to the second ATM switch 50. The second ATM switch 50 thereafter re-assembles and re-synchronizes the cells received over the multiple T-1 communication links. The second ATM switch 50 then transmits the re-assembled ATM cells over an outgoing high bandwidth communication link, such as another OC-3 link 60. Such a process of de-assembling and re-assembling cells communicated over multiple communication links is known as inverse multiplexing.
However, performing inverse multiplexing in a conventional manner is inefficient and expensive. Existing hardware components with each ATM switch need to be modified or reconfigured. Furthermore, an additional inverse multiplexing chip or module needs to be added to de-assemble the cells received over a high band-width communication link and to re-assemble the cells received over a number of slower band-width communication links. Otherwise, the sequence of cells within a communicated stream may be altered and the integrity of the transmitted data destroyed. Unfortunately, making such changes to the associated hardware components within each ATM switch are expensive and inefficient. For example, it requires a new physical sub-layer called Inverse Multiplexing for ATM (IMA) Transmission Convergence Sub-layer (IMA TC) between the presently defined TC sub-layer and ATM layer.
Accordingly, there is a need for a mechanism to provide more efficient and easier inverse multiplexing.